Brain metastases (BMs) are a common complication of advanced breast cancer (BC), and their management has significantly evolved. We evaluated the clinical impact of these changes dividing patients diagnosed with BCBMs at three Institutions according to year of BMs diagnosis: 2000-2007 (group A), 2008-2014 (group B) and 2015-2022 (group C). Stereotactic radiotherapy increased (p < 0.001), and WBRT decreased (p = 0.010) over time. Among HER2+ BC patients, more received anti-HER2 therapy after BM diagnosis in recent years (p < 0.011). Overall survival (OS) did not improve in the entire cohort (p = 0.260); however, OS improved in patients with HR-/HER2+ BC (median OS 8.7, 10.1, 23.7 months in group A, B, C, respectively; p = 0.002). HER2-positivity, not prognostic in group A, became prognostic in group C (p < 0.001). While therapy for patients with BCBMs significantly changed over two decades, an OS improvement was observed only in HR-/HER2+ patients, potentially due to increased availability of anti-HER2 therapies with intracranial activity.

Tumor heterogeneity represents a major challenge in breast cancer, being associated with disease progression and treatment resistance. Precision medicine has been extensively applied to dissect tumor heterogeneity and, through a deeper molecular understanding of the disease, to personalize therapeutic strategies. In the last years, technological advances have widely improved the understanding of breast cancer biology and several trials have been developed to translate these new insights into clinical practice, with the ultimate aim of improving patients' outcomes. In the era of molecular oncology, genomics analyses and other methodologies are shaping a new treatment algorithm in breast cancer care. In this manuscript, we review the main steps of precision medicine to predict drug sensitivity in breast cancer from a translational point of view. Genomic developments and their clinical implications are discussed, along with technological advancements that could broaden precision medicine applications. Current achievements are put into perspective to provide an overview of the state-of-art of breast cancer precision oncology as well as to identify future research directions.

Despite potential clinical implications, the complexity of tumor immune microenvironment (TIME) of breast cancer (BC) brain metastases (BMs) is still poorly understood. We previously reported that a higher CD4+FoxP3+/CD8+ cell ratio in the stromal compartment and a higher density of CD163+ M2-polarized macrophages are associated with worse overall survival in BCBMs. We here assess the evolution of TIME from primary BC to paired BMs using multiplex immunofluorescence. TIME profiling of archival FFPE specimens of paired primary BC and BMs from 25 patients was carried out using two multiplex immunofluorescence panels (CD4, CD8, Granzyme B, FoxP3, CD68, pan-cytokeratin, DAPI; CD3, PD-1, PD-L1, LAG-3, TIM-3, CD163, pan-cytokeratin, DAPI). Variations in immune cell densities were assessed using a paired Wilcoxon test. In both the tumor and stromal compartment, BMs exhibited a more immunosuppressive TIME with significantly lower lymphocytic (CD3+), T cell (CD8+), and cytotoxic cell (GranzymeB+) infiltration (p<0.001), higher CD4+FoxP3+ infiltration (p<0.001), and a higher CD4+FoxP3+/CD8+ ratio (p<0.01) as compared to primary tumors. Moreover, the lymphocytic infiltrate presented a more immune exhausted phenotype, with higher levels of CD3+PD-1+ (p<0.01) and CD3+PD-1+LAG3+ (p<0.05) cells, in BMs as compared to primary BCs. PD-L1 expression in the tumor compartment was also reduced in BMs compared to primary BCs (p<0.001). In addition, TIM3+ cells were significantly less represented in both the tumor and stromal compartment (p<0.01) On the other hand, BMs presented significantly higher levels of macrophagic (CD68+) infiltration in the tumor compartment (p=0.008) and of CD163+ M2-polarized macrophagic infiltration in the stromal compartment (p<0.001), which was associated with a significant decrease in the CD3/CD163+ ratio in both compartments (p<0.001). Our results suggest that BCBMs present a more immunosuppressed TIME as compared to primary tumors, comprising immune phenotypes (e.g. immunosuppressive tumor-associated macrophages) that may represent a potential target for immunotherapeutic strategies for BCBMs.

Deleterious or likely deleterious gTP53m is a rare situation that increases the risk of many cancers, among which BC comes first for women. 12 years(y) ago, we published one of the first series that suggested an increased risk of 2ndM after RT among these women (Heymann, Rad Oncol 2010). The present study evaluated the long-term risk of any 2ndM among women with BC and gTP53m treated with RT. We retrospectively reviewed the medical records of women with gTP53m who were treated for a stage I-III BC at our referral tertiary center between 01/1982 - 04/2020. Outcomes assessed included the time interval between first BC and the occurrence of a local in-BC (outcome 1), a contralateral (CL) new primary BC (outcome 2) or a non-BC primary tumor (outcome 3), whichever occurred first. Patients (pts) were censored at the time of metastatic relapse and death. Among the 65 women included, median age at primary diagnosis was 33y. Invasive ductal carcinoma (72.3%), ER+ (56.6%) and HER2+ (43.4%) were the main tumor characteristics. 24 pts (36.9%) received adjuvant RT, 69.2% received chemotherapy, 41.5% HER2-directed treatments and 44.6% endocrine therapy. 21 pts had prophylactic mastectomy. After a median follow-up of 8.6y, 11 local recurrences, 16 contralateral BC, 21 other primaries, 13 metastatic relapses were observed. The table reports time-to-event outcomes. In the multivariable analysis, history of a previous cancer before BC (HR 0.39, 95%CI 0.157-0.97) but not RT (HR 0.92, 95%CI 0.46-1.84) was associated with the occurrence of 2ndM.Table: 163PProportion (%) of pts without the outcome of interest at 5, 10, 15yOutcome 1Outcome 2Outcome 35y86%80%87%10y81%73%73%15y76%73%42% Open table in a new tab . Pts with BC and gTP53m have a high risk of new cancer events, mostly driven by BC events. The current recommendation of a CL/bilateral prophylactic mastectomy remains of major interest. In this cohort, RT was not an independent predictor of 2ndM, but this study's power is limited. RT should not be formally contra-indicated among gTP53m carriers, but its benefit-risk ratio carefully assessed.

Significant discordance rates in HER2 status between primary breast cancer (BC) and brain metastases (BCBM) have been reported, potentially affecting clinical decision-making. Biological recharacterization of BCBMs is difficult due to inherent neurosurgery risks. We here assess the potential of radiomics to non-invasively assess HER2 status of BCBMs. We retrospectively identified BC patients from 2 centers, for which HER2 status evaluated on BCBMs (HER2-positive versus HER2-negative by ASCO-CAP) and preoperative brain MRI were available. A total of 218 radiomics features, complying with Imaging Biomarker Standardization Initiative feature definition, were extracted from manually segmented BCBMs using Python. Robust features (selected using LASSO) associated with HER2 status in univariate analysis (p<0.05) were tested in multivariate analysis. Linear regression model (LRM) and non-linear logistic regression model (NLRM) were constructed. Machine learning (ML) algorithms (decision tree, k-nearest neighbor, and support vector machine [SVM]), were tested, by spliting the dataset into 70% for training, 20% for testing, and 10% for validation. Classifiers were trained and tested using the cross-validation approach 10 times; median values for AUC, accuracy, sensitivity and specificity were obtained. The performance of the best classifiers was evaluated on the validation dataset. Analyses were performed using MATLAB R2021b Statistics and Machine Toolbox (MathWorks). We identified 54 BC patients, for which HER2 status evaluated on 56 BCBMs (HER2+ N=27, HER2- N=29) and preoperative brain MRI was available. At univariate analysis, 9 features were significantly associated with HER2 status, but diagnostic accuracy was low (maximum 67%). Using LRM and NLRM, including the 9 significant features at univariate analysis, accuracy increased to 79%. Using the ML approach, the best classifier among the pattern recognition approaches tested was a SVM including the 9 significant features, which reached an AUC of 0.97 and an accuracy of 91% and 86% on test and validation set, respectively. Radiomics using machine learning approach shows potential to non-invasively predict HER2 status of BCBMs.

Sequential anthracyclines (A) plus taxanes represent a standard adjuvant regimen for early TNBC patients. The potential risk for long-term toxicities led to studies exploring the use of A-free options with partly inconsistent results. We here addressed this question by conducting a non-inferiority meta-analysis. We queried Embase, MEDLINE, PubMed, ASCO, and ESMO proceedings to identify randomised clinical trials comparing A-free and A-based regimens. Given the differences in study design, we applied the raw number of events to calculate the risk ratios (RR) for recurrence or death. The non-inferiority (NI) margin was defined as the inverse of the product of the unconfounded treatment effects of A plus taxanes versus A, and A versus no chemotherapy, based on estimates from the EBCTCG 2012 meta-analysis on adjuvant chemotherapy. To improve the specificity, a conservative NI margin was defined using the upper bounds (UB) of the EBCTCG confidence intervals (CI). We retrieved 3,317 potentially eligible records and 8 studies were included in the meta-analysis (4,328 patients in total). The median follow-up time was in the range of 40-97 months. The RR for recurrence with A-free compared to A-based therapy was 1.06, with the UB of the 95% CI (0.93-1.21) falling within the NI margin (1.75). Using the conservative NI margin for recurrence (1.43), A-free regimens still proved non-inferior. A sensitivity analysis excluding trials using CMF as an A-free regimen showed similar results (RR 0.97, 95% CI 0.83-1.12). The RR for death from any cause with A-free compared to A-based therapy was 1.12, with the UB of the 95% CI (0.92-1.36) falling within the NI margin (1.4). A-free regimens did not prove non-inferior to A-based chemotherapy when using the 1.15 conservative NI margin. In the largest meta-analysis to date, A-free regimens proved non-inferior to A-based adjuvant therapy for risk of recurrence. However, non-inferiority could not be shown for risk of death when applying a conservative NI margin. These results may support the adoption of A-free regimens. The observed, substantial study heterogeneity calls for caution when interpreting these findings.

Although 1% is the recommended cutoff for defining triple-negative breast cancer (TNBC), growing evidence suggests that 10% cutoff may better recapitulate TNBC. Conversion to TNBC at relapse is associated with poor survival. We primarily aim to assess the prognostic impact of phenotypic conversion to estrogen receptor (ER)-low BC in patients experiencing relapse. Relapsing BC patients from two Institutions were included. Patients were categorized in: TNBC (ER=0%, HER2-0/low), ER-low (ER=1-9%, HER2-0/low), Luminal (ER=10-100%, HER2-0/low), HER2+. Overall survival (OS) and post-relapse survival (PRS) were adopted as endpoints. 877 patients were included. The proportion of ER-low tumors was 3.2% on primary BC and 2.9% on relapse. When assessing the prognostic impact of primary BC phenotype, TNBC and ER-low retained a similar and significantly poorer prognostic impact than Luminal and HER2+ BC. In detail, median OS [mos] was: TNBC 68.6, ER-low 47.6, Luminal 125.4, HER2+ 121.4, p<0.001). PRS analysis described the same phenomenon (p<0.001) Superimposable findings were observed when considering the prognostic impact of tumor phenotype at relapse (OS, p<0.001; PRS, p<0.001). At relapse, 6.4% of TNBC, 2.5% of Luminal and 1.9% of HER2+ primary BC cases switched to ER-low phenotype (overall conversion rate to ER-low BC: 2.8%). Among Luminal BC patients, those converting to ER-low at relapse showed the worst outcome, with poorer survival than those maintaining Luminal BC or converting to either TNBC or HER2+. In detail, median OS [mos] was: concordant Luminal 134.7, conversion to ER-low 54.4, conversion to TNBC 80.4, conversion to HER2+ 129.9, p<0.001; median PRS [mos] was: concordant Luminal 51.4, conversion to ER-low 12.4, conversion to TNBC 29.6, conversion to HER2+ 44.4, p<0.001. ER-low BC was associated with unfavorable prognosis, similar to TNBC and significantly poorer than Luminal and HER2+. Luminal BC patients converting to ER-low phenotype experienced the worst survival rates, even worse than those converting to TNBC, possibly due to the limited access to TNBC treatment algorithms. Our study supports the assimilation of ER-low BC to TNBC.

Background: In HER2+ breast cancer (BC) patients undergoing neoadjuvant treatment (NAT), higher levels of baseline TILs are associated with both increased rates of pathologic complete response (pCR) and improved survival. Data regarding the prognostic role of TILs on residual disease (RD) in patients failing to achieve pCR are conflicting. Material and Methods: HER2+BC patients treated with chemotherapy (CT) plus anti-HER2-based NAT at 3 Italian Institutions were included. RCB and stromal TILs (RD-TILs) were evaluated on post-NAT samples in case of no-pCR. RCB was considered both as a continuous and a categorical variable (classes I/II/III). The Harrell's c-index was used to determine the optimal prognostic cutoff for RD-TILs. The log-rank test was used to perform survival analyses and the Cox regression model to calculate hazard ratios (HRs) and 95% confidence intervals (CIs). C-indexes were evaluated to compare the performance of the prognostic models. Results: 295 HER2+BC patients were included. NAT consisted on anti-HER2 therapy+CT (83.3% anthracycline + taxane). 66.1% of patients (n = 195) had RD after NAT. RCB and RD-TILs were available for 180 and 159 patients, respectively. Mean and median RCB scores were 2.1 and 1.7; RCB class distribution was: I = 21.7%, II = 62.2%, III = 16.1%. Mean and median RD-TILs were 9.8% and 5.0%. 15% of RD-TILs was identified as the optimal prognostic cutoff for OS. The distribution of RD-TIL categories was: low (<15%) 82.4%, high (≥15%) 17.6%. RCB was significantly associated with OS (RCB score, p < 0.001; 5-year OS for RCB class I vs II vs III: 93.0% vs 86.3% vs 62.0%, p < 0.001). High RD-TILs were significantly associated with poorer OS (HR 2.32 [95%CI 1.07–5.03]; 5-year OS for high vs low RD-TILs: 67.9% vs 83.7%, p = 0.028). At multivariate analysis both RCB score and RD-TIL categories maintained their independent prognostic value for OS (RCB: HR 1.90 [95%CI 1.35–2.67] p < 0.001; RD-TILs: HR 2.30 [95%CI 1.06–5.01], p = 0.036). The combined score RCB + TIL was calculated from the estimated coefficient of each variable in the bivariate logistic model for OS: RD-TILs (0 = low/1 = high) × 0.83 + RCB (score) × 0.64. RCB + TIL score was significantly associated with OS (p < 0.001). The C-index of RCB-TIL score was numerically higher than that of RCB (0.73 vs 0.68, p = 0.08) and significantly higher than that of RD-TILs (0.73 vs 0.58, p = 0.007). Conclusions: We reported an independent negative prognostic impact of higher RD-TILs after anti-HER2+CT-based NAT which might potentially underly an unbalance of RD immune microenvironment towards immunosuppressive features. We also provided a new composite prognostic score based on RCB+TIL which was significantly associated with OS. The comparison of prognostic model performance revealed that RCB+TIL score was capable of providing additional prognostic information than either RCB (trend) or RD-TILs alone. Conflict of interest: Advisory Board: FM: Roche, Novartis, Gilead. GG: EliLilly, Novartis and Gilead. MF: Astellas Pharma, QED Therapeutics, Diaceutics, Tesaro, Roche, Eli Lilly, and Novartis. AZ: Pfizer, Roche, Novartis, Lilly, Daiichi Sankyo, Seagen, AstraZeneca, MSD, ExactSciences. VG: Amgen, Exact Sciences, Gilead, GSK, EliLilly, Merck Serono, MSD, Novartis, Pfizer, Sanofi. MVD: AstraZeneca, Daiichi Sankyo, EliLilly, Exact Sciences, Gilead, MSD, Novartis, Pfizer, Seagen.

In the last years we have witnessed tremendous advancements in the treatment landscape of metastatic breast cancer (MBC), leading to a progressive prolongation of progression-free survival and, in some cases, also of overall survival. This led to a substantial increase of advanced disease treatability. In the present review we comprehensively and critically describe the most significant progresses in the therapeutic scenario of MBC according to BC subtype. In particular, we reviewed studies reporting practice-changing data in hormone receptor-positive/human epidermal growth factor receptor 2 (HER2)-negative, HER2-positive and triple-negative BC, with also a hint to BRCA-related tumors and the emerging HER2-low-positive category.

HER2DX is a prognostic and predictive assay in early-stage HER2+ BC based on clinical data and the expression of 4 gene signatures (immune, proliferation, luminal differentiation and HER2 amplicon), including ERBB2 levels. Here, we evaluated the ability of HER2DX to predict efficacy of a de-escalated, chemotherapy (CT)-free neoadjuvant regimen in HER2+/HR+ BC.

In patients with triple-negative breast cancer (TNBC) undergoing neoadjuvant chemotherapy (NACT), higher tumor-infiltrating lymphocytes (TILs) strongly correlate with increased rates of pathologic complete response (pCR) and improved survival. The aim of the present work is to investigate the changes of TIL levels from baseline biopsy to residual disease (RD) in TNBC patients failing to achieve pCR after standard NACT with anthracycline-taxane (A-T) +/- carboplatin (Cb). TNBC (ER&PgR<10%) patients treated with neoadjuvant A-T +/-Cb failing to achieve pCR were included. Stromal TILs were evaluated on baseline biopsy and matched samples of RD. The non-parametric Wilcoxon test was applied to compare TIL levels from baseline biopsy to RD. 79 patients with matched samples of baseline TILs and RD-TILs were included: 62% treated with A-T, 38% with A-TCb. Mean and median baseline TILs were 8.8% and 5%; mean and median RD-TILs were 14.1% and 8%. The distribution of TIL categories in matched samples of baseline biopsy and RD is shown in the table. RD-TILs were significantly higher than baseline TILs in the overall population (p=0.004) and in both A-T (p=0.027) and A-TCb subgroups (p=0.043). A significant increase of TIL levels after NACT was also seen in patients with low baseline TILs, in the overall population (p<001) and in both treatment subgroups (A-T, p=0.002, A-TCb, p=001).Table: 26PRDLow TILs (%)Intermediate TILs (%)High TILs (%)BaselineLow TILs (%)45 (57)15 (19)2 (2.5)Intermediate TILs (%)6 (7.6)10 (12.7)1 (1.3)High TILs (%)000TILs categories have been classified according to cutoffs suggested by Denkert et al, 2018 (low: 0-10; intermediate: 11-59; high: ≥60). Open table in a new tab TILs categories have been classified according to cutoffs suggested by Denkert et al, 2018 (low: 0-10; intermediate: 11-59; high: ≥60). We reported in a population of TNBC patients failing to achieve pCR after standard NACT, that A-T +/- Cb is capable of enhancing tumor immune infiltration from pre-treatment tumor to RD. Importantly, we observed that TIL infiltration was enhanced after A-T +/- Cb also in patients with "immune-cold" tumors at baseline.

HER2 positivity is a driver of endocrine resistance in hormone receptor-positive (HR+) breast cancer (BC). However, clinical data suggests the existence of a subset of HR+/HER2+ BC that might be endocrine sensitive with a natural history similar to HR+/HER2-, especially when HER2 signaling is blocked. Given the scarcity of data on genomic bases of endocrine sensitivity in HR+/HER2+ BC, we planned this gene expression analysis in the context of the PerELISA trial. Our aim is to characterize genomic features associated with endocrine sensitivity in HR+/HER2+ BC. PerELISA is a multicentric neoadjuvant phase II trial that evaluated the efficacy of a chemotherapy-free regimen based on dual HER2 blockade (trastuzumab-pertuzumab) in combination with letrozole in HR+/HER2+ BC selected on the basis of Ki67 response after 14 days of letrozole alone (Guarneri, Ann Oncol 2019). Endocrine sensitivity was defined by protocol as relative Ki67 reduction ≥20% from baseline at day 14 (antiproliferative response). Expression of 555 genes on baseline tumor samples from 56 patients was quantified by nCounter platform. Using unpaired two-groups SAM analysis (FDR<1%), we identified 13 genes overexpressed in endocrine sensitive as compared to non-endocrine sensitive BC (NAT1, RERG, SCUBE2, RGS22, ERBB4, PGR, ADRA2A, H19, ESR1, IKBKB, CA12, CELSR1, IL6ST). No underexpressed gene was identified with FDR <1%. A published signature of RB loss (RBsig), previously reported to potentially predict resistance to CdK4/6 inhibitors in HR+/HER2- BC and to be associated with pCR rates in HR+/HER2+ BC treated with neoadjuvant chemotherapy (Malorni, Oncotarget 2016) was computed. RBsig levels were significantly lower in endocrine sensitive as compared to non-endocrine sensitive BC (t-test p=0.007). A subgroup of HR+/HER2+ BC is sensitive to endocrine treatment, showing biological processes similar to those identified in HR+/HER2- BC. These patients might potentially represent ideal candidates for trials testing CdK 4/6 inhibitors in HR+/HER2+ BC.

Approximately a half of breast tumors traditionally classified as HER2-neg exhibit HER2-low expression (IHC 1+ or 2+ and ISH neg.). We recently described a high instability of HER2-low expression from primary breast cancer (BC) to relapse (Miglietta F et al., ESMO Breast Cancer 2021). Aim of this study is to track the evolution of HER2-low expression from primary BC to residual disease (RD) after neoadjuvant treatment. Patients undergoing neoadjuvant treatment with available baseline tumor tissue and matched samples of RD (in case of no pCR) were included. HER2 expression was evaluated according to ASCO/CAP recommendations in place at the time of diagnosis. Cases diagnosed between 2007 and 2013 were reviewed to comply with the 10% cutoff of IHC for HER2-positivity. HER2-neg cases were further classified as HER2-0 or HER2-low (IHC 1+ or 2+ and ISH neg.). 447 patients were included. Primary BC phenotype was: HR-pos/HER2-neg 23%, triple-negative (TN) 35%, HER2-pos 42%. HER2-low cases were 56% of the HER2-neg cohort and were significantly enriched in the HR-pos/HER2-neg vs TN subgroup (69% vs 47%, p=0.001). In patients failing to achieve pCR after neoadjuvant treatment (n=292), the overall rate of HER2 expression discordance was 27%, mostly driven by cases converting either from HER2-0 primary BC to HER2-low RD (9%) or from HER2-low primary BC to HER2-0 RD (15%; Table). Overall, 36% of non-pCR patients had a HER2-low expression on RD, including 12% of patients with TN and 24% of patients with HR-pos/HER2-neg disease. Among HR-pos/HER2-neg patients with HER2-low expression on RD, 23% had an estimated high risk of relapse according to the residual proliferative cancer burden (RPCB class 3).Table: 212PPrimary tumorResidual diseaseHER2-0HER2-lowHER2-posTotaln%n%n%n%HER2-05117269007726HER2-low431570241<111439HER2-pos0083933210135Total9432104369432292100 Open table in a new tab HER2-low expression showed high instability from primary BC to RD after neoadjuvant treatment. HER2-low expression on RD may guide personalized adjuvant treatment for high-risk patients in the context of clinical trials with novel anti-HER2 antibody-drug conjugates.

About a half of breast cancers traditionally classified as HER2-negative show a low HER2 expression (IHC 1+ or IHC 2+ and ISH negative) that can be targeted by new antibody-drug conjugates. There is no data on the evolution of HER2-low status from primary tumor to relapse. Patients with matched primary and relapsed breast cancer samples from two Institutions (IOV-IRCCS Padova and Treviso Hospital) were included. HER2 was evaluated according to ASCO/CAP recommendations in place at the time of diagnosis. Cases diagnosed between 2007 and 2013 were reviewed by IHC to comply with the cut-off of >10% cells staining for HER2 positivity. Moreover, 100 random samples were reviewed by a blinded pathologist: agreement with the original report was 80%. HER2-neg cases were sub-classified as HER2-low (IHC 1+, or IHC 2+ and ISH not amplified), or HER2-0 (IHC 0). 575 patients were included. Primary tumor phenotype was: 59% luminal-like (HR+/HER2-neg), 25% HER2-pos, 16% triple-negative. The proportion of HER2-low cases was 34% on the primary tumor and 38% on the relapse samples. Among HER2-neg cases, HER2-low status was more frequent in Luminal-like vs triple-negative tumors (47% vs 41% on primary tumor samples, p=0.268; 54% vs 40% on relapse samples, p=0.006). The overall rate of HER2 discordance was 38% (Table), mostly represented by HER2-0 switching to HER2-low (15%) and HER2-low switching to HER2-0 (14%). A minority (9%) of cases lost or acquired HER2-positivity. Among patients with a primary HER2-neg tumor, the rate of HER2 discordance was higher in luminal-like vs triple-negative cases (45% vs 35% p=0.080). This difference was mostly driven by cases switching from HER2-0 to HER2-low: 40% of luminal-like/HER2-0 vs 24% of triple-negative/HER2-0 patients (p=0.088).Table: 4MO_PRRelapseHER2-0HER2-lowHER2-positiveTotalPrimary tumourn%n%n%n%HER2-013423%8515%132%23240%HER2-low7814%10919%92%19634%HER2-positive61%234%11820%14726%Total21738%21838%14024%575100% Open table in a new tab HER2-low expression is highly unstable during disease evolution. Relapse biopsy in case of a primary HER2-0 tumor may open new opportunities for treatment in a relevant proportion of patients.

Despite clinical implications, the complexity of immune microenvironment in breast cancer (BC) brain metastases (BM) is still poorly understood. Multiplex immunofluorescence (mIF) simultaneously visualizes several IF labeled proteins while maintaining spatial information and can be used to identify spatially interacting cells, potentially providing useful information to guide therapeutic approaches.

Abemaciclib is approved for HR+/HER2- metastatic breast cancer in combination with endocrine therapy (ET). We evaluated safety and efficacy of abemaciclib in association with ET in a single-institution cohort. Patients with HR+/HER2- metastatic breast cancer treated with abemaciclib in combination with ET as first or second line between April 2019 and November 2020 at Istituto Oncologico Veneto of Padova were identified. Clinicopathological characteristics, adverse events and their grade (according to CTCAE 5.0 criteria) were collected. Objective response rate (ORR) according to RECIST 1.1 was also evaluated. 72 patients were included: 52 received abemaciclib as first line, 20 as second line; in 49 patients abemaciclib was administer in combination with an aromatase inhibitor, in 23 with fulvestrant. 95.8% of patients experienced at least one adverse event. The most common was diarrhea (79.2%), mainly G1 (66.7% of cases). Other common toxicities were: neutropenia (56.9%), increased serum creatinine (38.9%), anemia (37.5%), nausea (34.7%), fatigue (23.6%) and hypertransaminasemia (22.2%). Toxicities were mainly low grade; 10.1% of adverse events where G3-4. 48.6% of patients required a temporary interruption of abemaciclib and 45.8% a dose reduction. All 17 patients aged ≥70 required a dose reduction. A concomitant palliative radiotherapy was administered in 16 patients: in all cases radiotherapy was regularly completed; a temporary interruption of abemaciclib was required in 3 patients due to hematologic toxicities. In patients with measurable disease, ORR was 55.7%, significantly higher in first line compared to second line (70.5% vs 17.7%, p<0.001). ORR was not significantly different between full and reduced dose (46.9% vs 65.5%, p=0.143). At the time of the present analysis, 51 patients are still on therapy. Treatment discontinuations were due to disease progression in 17 patients, and to adverse events in 4 (G3 increased ALT in 1 patient and persistent G2-3 cutaneous toxicity in 3 patients). In a real-world population, abemaciclib was associated with a meaningful rate of objective response, with a favourable safety profile. Side effects were mostly low grade, manageable with temporary interruptions or dose reductions.

PT are rare fibroepithelial tumors accounting for < 1% of all breast tumors. We assessed clinicopathological features and their prognostic effect in a single-institution patients cohort. Patients diagnosed with PT between 2001 and 2008 at our Institution were identified. Clinical, surgical and pathological features were collected. Phyllodes-related relapse (PRR) was defined as locoregional or distant recurrence (contralateral excluded). 115 patients with benign, 30 with borderline and 21 with malignant PT were identified. Features associated with malignant PT were: younger age, larger T size, higher mitotic count, marked cytologic atypia, stromal overgrowth, stromal hypercellularity, necrosis and heterologous differentiation (all p<0.01). The majority of malignant PT patients received mastectomy (63.2% vs 3% of benign/borderline, p<0.001) and had negative surgical margins (83.3%). 4-yr cumulative PRR incidence was 7% for benign/borderline and 21.3% for malignant PT (p=0.107). In the entire cohort, marked cellular atypia and heterologous differentiation were associated with worse PRR-free survival (HR 14.10, p=0.036 for marked vs mild atypia; HR 4.21, p=0.031 for heterologous differentiation present vs absent). For patients with benign PT larger tumor size was associated with worse PRR-free survival (HR 9.67, p=0.013 for T>5cm vs T<2cm,). Positive margins were a poor prognostic factor for malignant PT patients (HR 16.61, p=0.025). Overall, 4 patients died because of PT: 3 patients with malignant and 1 with borderline PT. Patients with malignant PT had increased rates of PRR and phyllodes-related death. Cellular atypia and heterologous differentiation were poor prognostic factors in the entire cohort; large tumor size and positive margins were associated with increased risk of PRR in benign and malignant PT, respectively.